The invention relates to an inverter for feeding power of a direct voltage source, in particular of a photovoltaic generator, into an AC voltage mains, with an asymmetrically clocked bridge circuit having at least two first switches clocked at mains frequency and at least two second switches clocked at a higher clock rate.
Inverters in full bridge circuit are known. They can be implemented as one-phase or as three-phase full bridges for feeding into a grid. Each bridge branch consists of two switches in the event of one-phase feeding. A mains choke is located in the AC lines. In principle, the switches of the bridge circuit can be connected symmetrically or asymmetrically.
In order to decouple the arrangement from the DC side, the document DE 10 2004 030 912 B3 proposes to connect a fifth switch between the positive pole of the DC source and the two bridge branches. This additional, fifth switch is connected at high frequency and simultaneously to a respective one of the two lower switches of the bridge branches, whilst a respective one of the upper switches of the bridge branches is closed for each half wave of the mains voltage. Here, the switches are clocked asymmetrically.
Another arrangement is known from WO 2008 015 298 A1. This document describes a full bridge array with a divided intermediate circuit at the input. In each DC line between an intermediate circuit and a bridge, there is one series-connected switch. These switches are alternatively clocked at high frequency but at the same time with a respective one of the two lower switches of the bridge branches whilst a respective one of the upper switches of the bridge branches is closed for each half wave of the mains voltage. Clocking is also asymmetric here. An additional freewheel path is formed from two series connected diodes that are connected upstream of the bridge and the center tap of which is connected to the center tap of the intermediate circuit.
Three level arrays are also known. In this circuit topology, one bridge branch consists of four switches. The two central switches are bridged by two series-connected diodes during freewheel times. This circuit has the advantage that the voltage load of the active switches is reduced.
On inverters of this kind, one usually utilizes switches such as IGBTs or MOSFETs.